The skeletal response to a metabolic bone disease or a treatment regimen may be non-homogeneous. A particular disease or treatment may cause bone loss preferentially in the cortical or the trabecular bone, preserving one at the expense of the other. In the elderly osteoporotic population, we must be cognizant of the fact that a course of treatment with multiple therapies may have an effect on the skeleton which is not the sum of the individual parts. Non-invasive bone mass measurements can provide information about isolated regional skeletal responses, and this information can be used in a clinical setting to study the effects of specific disease processes or treatment regimens. The long-term goal of this program is to use information generated from patient studies to develop a comprehensive management plan for the treatment of the patient with multiple disorders. The experimental approach is designed to study "isolated" processes in vivo which are known to affect the skeleton in diverse ways. This information will be used to predict the effects of treatment when multiple metabolic stimuli are present, and this will be tested initially in a single population. Concurrently, the capability of the various bone mass measurements (quantitative computed tomography, dual-photon and single-photon absorptiometry, radiogrammetry) will be assessed individually and in concert for their ability to predict the clinical consequence of bone loss, that is, fracture. This capabililty of skeletal assessment coupled with the knowledge of the effects of various metabolic stimuli will allow a coherent approach to the management of the older osteoporotic patient.